Underground Ductile Pipe Fittings

[martin888888]

I have an underground 8" DIP water line with another 8" process line running parralle 2.5' away at same CL EL. I want to place a MJ Tee on the waterline and then a 45 MJ Fitting to dive it under the proccess line. What is minimum length of pipe normally needed to fit between 2 MJ fittings and still use mechanical restraint glands (eg megalugs)? Just trying to see if the 2.5' seperation is to close to allow the waterline to be diverted underneath it.

 

[bimr]

Some organizations have rules of thumb of 18-Inches, perhaps in the belief that the joint somehow damages the pipe but I don't know if there is any science that supports that.

The bolts on 8-Inch pipe require 5-Inches of clearance to install. So you can use a 12-Inch long pipe spool as a minimum.

http://www.ebaa.com/files/pdf/brochures/Brochure.2100.pdf

It does depend somewhat on the particular manufacturer's joint that you are using, but the megalug joint for example does not transmit radial forces onto the pipe. EBBA Iron states that the thrust load is primarily longitudinal.

Here is a brochure describing the history of the megalug for ductile iron pipe:

http://www.ebaa.com/files/pdf/connections/Connections.DI-02.pdf

The wedges on the megalug are typically 4 to 5-inches apart which gives an indication of the zone of influence of the restraint on the pipe.

EBBA Iron also states that the joint does not damage the pipe:

"All of these tests prove that the 2000PV design works and the product does not damage the pipe in any way. Pipe that has been tested with the 2000PV can actually perform better than pipe without joint restraint. The long term tests at elevated pressures prove there is no immediate or long term damage to the pipe. Cyclic testing provides an accelerated method of determining
whether or not an attachment will cause premature failure of the pipe. The cyclic testing done on the 2000PV proves that there is no damage done to the pipe by utilizing the 2000PV as a joint restraint system."

If you were using a different brand than megalug, it is probably best to call the manufacturer of the restraint that you plan to use and get technical advice.

 

[martin888888]

Thanks for the great info. Sounds like you can get away with a 12" spool piece between the two mech joints. Do you think they would make that 12" pipe connection in the field?

 

[martin888888]

I guess the tee doesnt have to come straight out either, you can turn it down to get under the pipe quicker. Stupid question, I am not a big piping guy, when you say spool piece does that refer to just a small 12" section of pipe that will fit between the two MJ's? By spool piece I always think of a prefabricated flange and small pipe connection that is pre made and brought to the site.

 

[rconner]

It sounds like what you likely need is a short plain end by plain end pipe (sometimes also called a "pup") to go in between mechanical joint fitting bells and dip down to a lower invert elevation under the parallel line. While short pipes can be pre-fabricated for a price and delivery, most installers would prefer to field cut such a small diameter cut pipe from another pipe (maybe in 10 minutes or less with an abrasive saw). Guidance for minimum clearance between buried ductile iron pipes and structures, including other pipelines, can be found in ANSI/AWWA Standard C600.